Calcium oxalate deposition in renal allografts: morphologic spectrum and clinical implications

Many aspects of calcium oxalate (CaOx) deposition in renal transplant biopsies are not known. Review of all renal transplant biopsies performed in a 7-year period showed that CaOx deposition could be classified into three groups. Group I: Seven biopsies within a month post-transplant displayed rare CaOx foci against a background of acute tubular necrosis or acute cell-mediated rejection. At follow-up, five grafts functioned well and two failed due to chronic allograft nephropathy. CaOx in this context was an incidental finding secondary to a sudden excretion of an end-stage renal disease-induced increased body burden of CaOx. Group II: Two biopsies performed 2 and 10 months post-transplant showed rare CaOx foci against a background of chronic allograft nephropathy, leading to graft loss. CaOx in this context reflected nonspecific parenchymal deposition due to chronic renal failure regardless of causes. Group III: One biopsy with recurrent PH1 characterized by marked CaOx deposition associated with severe tubulointerstitial injury and graft loss 6 months post-transplant. There were two previously reported cases in which CaOx deposition in the renal allografts was due the antihypertensive drug naftidrofuryl oxalate or increased intestinal absorption of CaOx. CaOx deposition in renal allografts can be classified in different categories with distinctive morphologic features and clinical implications.